can someone tell me how I check the power steering fluid on my 1990 190E? Do I just twist the black knob on top? What fluid do I add? I hear that ATF will work (which type and brand?). Should I just stick with what the manual says--don't know what it recommends though. Thanks!

if you don't go to the dealership be sure to specify that your car is a mercedes (or at least a european car). I believe that the "regular" power steering fluid for domestic and/or japanese cars are of a different specification and may cause issues in the future.